1. Field of the Invention
The present invention relates to a direct current (DC) output power supply which implements an automatic power-balancing scheme enabling it to operate from two input voltage ranges. In particular, this invention achieves this duality by connecting the inputs of two power converters in either series or parallel, according to voltage supply level, and providing a balance winding unit to compensate for any power imbalance generated during operation.
2. Description of Related Art
With the increasing popularity of computers and other electronic devices over the past few years, the demand for power conversion power supplies that convert alternating current (AC) into DC has also increased. Although conventional power conversion supplies are limited to operating within one particular input voltage level, the voltage available to operate these power supplies often comes in two distinct ranges. In order for conventional power supplies to continuously operate over two input voltages, power semiconductors must be selected according to their functionality at both voltage levels. In particular, these semiconductors must simultaneously meet the voltage rating requirements of operating at the higher input voltage and the current rating requirements of operating at the lower input voltage. Semiconductors with such characteristics are very expensive though, making this design undesirable. Also, in order to meet requirements of several safety agencies, such as Underwriters Laboratories (UL), the Canadian Standards Association (CSA), and Technischer Uberwachungs-Verein (TUV), the physical spacing between primary windings and safety extra low voltage (SELV) windings inside the transformers must be designed for voltages associated with the higher input voltage range.
The most commonly used method for achieving the aforementioned duality is to switch the power supply from operating as a full-wave rectifier to a voltage doubler. In particular, these circuits provide for the automatic configuration of a power supply by switching between these two modes of operation in response to either a low AC input voltage level VIN or a high AC input voltage level 2 VIN. More specifically, these circuits operate as voltage doublers when the AC input signal is VIN, and as full-wave rectifiers when the AC input signal is 2 VIN. When operating as a full-wave rectifier, these circuits simply create a DC equivalent to the AC input signal and pass it through the remainder of the circuit. When operating as a voltage doubler, these circuits create a rectified signal that is two times larger than the AC input signal. Limitations to this design include its need for separate circuits to accommodate this bimodal operation. These circuits are, however, somewhat complicated and often require excessive hardware.
Accordingly, it would be very desirable to provide a simplified power supply, which implements an automatic power-balancing scheme, to operate from two input voltage ranges.
The present invention is directed to a simplified dual input power supply that avoids the complexities of prior art power supplies through the implementation of an automatic power-balancing scheme.
In an embodiment of the invention, a power supply comprises a first power converter having respective input and output terminals, and a second power converter having respective input and output terminals. The output terminals of the first and second power converters are connected in series to provide a combined output voltage. A switch is connected to the input terminals of the first and second power converters. The switch has a first state by which the input terminals of the first and second power converters are connected in series, and a second state by which the input terminals of the first and second power converters are connected in parallel. A pulse width modulator (PWM) unit provides a drive signal to regulate current provided to the first and second power converters. The automatic power-balancing scheme is provided by a balance winding coupled between the first and second power converters in order to share power between these two converters when their inputs are connected in series.
A more complete understanding of the dual input power range power supply will be afforded to those skilled in the art, as well as a realization of additional advantages and objects thereof, by a consideration of the following detailed description of the preferred embodiment. Reference will be made to the appended sheets of drawings, which will first be described briefly.